There has been proposed a digital broadcast receiver, which refers to an EIT (Event Information Table) included in information of a program being viewed to determine presence or absence of sub-audio, and which, when the result of determination is that sub-audio is present, displays an OSD image indicating the presence of sub-audio (for example, Patent Document 1). Specifically, the digital broadcast receiver determines presence or absence of sub-audio by determining whether the EIT includes sub-audio information. This digital broadcast receiver enables a viewer to recognize presence or absence of sub-audio and to reproduce sub-audio when necessary.
There has been also proposed a digital broadcast receiver which refers to a PMT (Program Map Table) included in program information to determine presence or absence of sub-audio. With reference to FIG. 16, this digital broadcast receiver will be described in detail. FIG. 16 is a diagram illustrating a configuration of the digital broadcast receiver which determines presence or absence of sub-audio with reference to a PMT.
In FIG. 16, a digital broadcast receiver 2 is connected to an antenna 1 and includes a receiving section 21, a signal separating section 22, an audio generating section 23, an audio reproducing section 24, a video generating section 25, a video display section 26, and a control section 27.
The receiving section 21 decodes a digital broadcast signal that is received by the antenna 1, and outputs to the signal separating section 22 a transport stream that is a decoded digital broadcast signal. The digital broadcast signal is a signal in which an audio signal including a main audio signal and a video signal are multiplexed, or a signal in which an audio signal including a main audio signal and a sub-audio signal, and a video signal are multiplexed.
The signal separating section 22 separates, from the transport stream inputted thereto, a main audio data stream (main audio stream) that is a main audio signal, a video data stream (video stream) that is a video signal, and program information data. When a sub-audio data stream (sub-audio stream) that is a sub-audio signal is included in the transport stream inputted thereto, the signal separating section 22 further separates the sub-audio stream from the inputted transport stream. Then, the signal separating section 22 outputs the main audio stream having been separated to the audio generating section 23, and outputs the video stream having been separated to the video generating section 25. The signal separating section 22, when it has further separated the sub-audio stream, outputs the sub-audio stream having been separated to the audio generating section 23.
As shown in FIG. 17, the audio generating section 23 includes a main audio decoding section 231, a sub-audio decoding section 232, and an audio synthesizing section 233. FIG. 17 is a diagram illustrating a specific configuration of the audio generating section 23. The main audio decoding section 231 decodes the main audio stream inputted thereto to generate a decoded main audio signal that can be reproduced, and outputs the decoded main audio signal to the audio synthesizing section 233. The sub-audio decoding section 232 decodes the sub-audio stream inputted thereto to generate a decoded sub-audio signal that can be reproduced, and outputs the decoded sub-audio signal to the audio synthesizing section 233. In accordance with a control of the control section 27, the audio synthesizing section 233 synthesizes the decoded main audio signal and the decoded sub-audio signal to output the synthesized signal to the audio reproducing section 24, or outputs only the decoded main audio signal to the audio reproducing section 24.
The audio reproducing section 24 is configured by, for example, a speaker. On receipt of the synthesized signal of the decoded main audio signal and the decoded sub-audio signal from the audio synthesizing section 233, the audio reproducing section 24 reproduces the main audio and the sub-audio simultaneously. On the other hand, when only the decoded main audio signal is received from the audio synthesizing section 233, the audio reproducing section 24 reproduces only the main audio.
As shown in FIG. 18, the video generating section 25 includes an OSD image output section 251, a video decoding section 252, and a video synthesizing section 253. FIG. 18 is a diagram illustrating a specific configuration of the video generating section 25. In accordance with a control of the control section 27, the OSD image output section 251 outputs an OSD image signal indicating the presence of sub-audio to the video synthesizing section 253, or does not output the OSD image signal. The video decoding section 252 decodes the video stream that is received from the signal separating section 22, and outputs the decoded video signal that can be displayed to the video synthesizing section 253. In accordance with a control of the control section 27, the video synthesizing section 253 synthesizes the OSD image signal and the decoded video signal to output the synthesized signal to the video display section 26, or outputs only the decoded video signal to the video display section 26.
The video display section 26 is configured by, for example, a display. On receipt of the synthesized signal of the OSD image signal and the decoded video signal from the video synthesizing section 253, the video display section 26 displays an OSD image on a broadcast video. On the other hand, when only the decoded video signal is received from the video synthesizing section 253, the video display section 26 displays only the broadcast video.
The control section 27 obtains, at a predetermined timing, a PMT included in the program information data having been separated by the signal separating section 22. Then, the control section 27 determines presence or absence of sub-audio by determining whether the obtained PMT includes sub-audio information.
When the result of determination is that the sub-audio is absent, the control section 27 controls the OSD image output section 251 so as not to output the OSD image signal while controlling the video synthesizing section 253 so as to output only the decoded video signal. Accordingly, the video display section 26 displays only the broadcast video. The control section 27 further controls the audio synthesizing section 233 so as to output only the decoded main audio signal to the audio reproducing section 24. Thus, the audio reproducing section 24 reproduces only the main audio.
When the result of determination is that the sub-audio is present, the control section 27 controls the OSD image output section 251 so as to output the OSD image signal while controlling the video synthesizing section 253 so as to synthesize the OSD image signal and the decoded video signal and output the synthesized signal. Accordingly, the video display section 26 displays the OSD image on the broadcast video. The control section 27, when it has accepted an instruction to reproduce the sub-audio from a viewer who saw the OSD image displayed on the broadcast video, controls the audio synthesizing section 233 so as to synthesize the decoded main audio signal and the decoded sub-audio signal and output the synthesized signal. Accordingly, the audio reproducing section 24 reproduces the main audio and the sub-audio simultaneously.
As described above, the conventional digital broadcast receiver determines presence or absence of sub-audio with reference to an EIT and/or a PMT included in the information of a program being viewed, and when the result of determination is that the sub-audio is present, it displays an OSD image indicating the presence of sub-audio.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-151214.